Third European Space Weather Week: 13-17 November 2006, Brussels, Belgium
Solar Cycle Electron
Radiation Environment at
GNSS Like Orbit
A. Sicard-Piet (1), S. Bourdarie (1) , D. Boscher (1), R. Friedel (2) , T. Cayton (2) ,
E. N. Sosnovets (3) , V. Kalegaev (3) , R. Ecoffet (4) , G. Rolland (4)
(1) ONERA/DESP, Toulouse, France
(2) Los Alamos National Laboratory, USA
(3) MSU, Russian Federation
(3) CNES, Toulouse, France
Outline
 Data Analysis
- Data set (GPS Navstar, Glonass-94)
- Contamination, Saturation
 Construction of the model
- Method used
- Comparison with POLE model
- Comparison with AE8 model
 Conclusions and Perspectives
Data Analysis : Data Set
 GPS-NS18
 GPS-NS28
 GPS-NS24
 GPS-NS33
Only the five first energy
channels have been used
Difficulty in GPS/BDD-II data
analysis:
250
GLONASS-94/DIERA2
GPS-NS33 / BDD2
200
F10.7 (W.m-2.Hz-1)
1) Over the period from 1990 to
present, 4 GPS Navstar satellites,
equipped with BDD-II particles
detectors which measure energetic
electrons, were flown:
GPS-NS28 / BDD2
150
GPS-NS24 / BDD2
100
50
GPS-NS18 / BDD2
0
janv-88
janv-92
janv-96
janv-00
janv-04
date
- Energy channels are different for each GPS satellite
- For two satellites, energy channels change during the period of the satellite (NS-24
and NS -28)
2) A Russian spacecraft, with nearly the same orbit than GPS Navstar : GLONASS-94,
equipped with DIERA2 particles detector measured 0.8-1.2 MeV electrons between
1994/06/04 and 1996/09/09.
Data Analysis : Data Set
GPS-NS24
Ele > 0.8 MeV
(cm-2.s-1.sr-1)
GPS-NS28
Ele > 0.8 MeV
(cm-2.s-1.sr-1)
GLONASS-94
Ele 0.8-1.2 MeV
(MeV-1.cm-2.s-1.sr-1)
Data Analysis : Saturation, contamination
The method used to analyze GPS/BDD-II and GLONASS-94/DIERA2 data in term of
saturation and contamination is compliant with the guidelines of COSPAR PRBEM:
data analysis procedure.
Saturation of the data
Ele. > 0.28 MeV (cm-2.s-1.sr-1)
Saturation
NS24/BDD2 1992/04/29 -1996/04/18
107
10-1
10-2
105
10-3
103
3
5
L
7
9
 Saturation: Electron flux is limited to certain value which cannot be
exceeded (~ 107 cm-2.s-1.sr-1) while the percentage of points increases.
Data Analysis : Saturation, contamination
Data contamination
GOES
08
GOES-08
Protons
Protons
80-165 MeV
80-165 MeV
GPS-NS-33
GPS-NS-33
Electrons
Electrons
> 1.32 MeV
> 1.32 MeV
Ele > 0.50 MeV (cm-2.s-1.sr-1)
Contamination
106
NS24/BDD2 1996/05/02 -2000/10/26
105
Contamination
104
103
10-4
10-3
10-2
10-1
100
GOES- 08 Pro 80-165 MeV (cm-2.s-1.sr-1.MeV-1)
 The contamination of GPS/BDD-II electron channels by protons from solar flares is
characterized by a correlation between measurements of GPS electron channels and
protons from GOES data.
Construction of the model : Method used
Interpolation in energy
Problems: - Energy channels of GPS Navstar satellites are different from one
satellite to another.
- Drift in energy
Solutions:  Definition of a grid in energy and interpolation in this grid
Calculation of yearly averaged electrons fluxes along GNSS orbit
(Only the years with more than 70 % of data of good quality are kept)
1,E+07
1,E+04
1,E+03
1,E+02
1,E+01
1985
-1
1,E+06
0.28 MeV
0.40 MeV
0.56 MeV
0.80 MeV
1.12 MeV
-1
1,E+05
-2
0.28 MeV
0.40 MeV
0.56 MeV
0.80 MeV
1.12 MeV
1.60 MeV
2.24 MeV
3.2 MeV
1,E+06
Flux (cm .s .sr )
-2
-1
-1
Flux (cm .s .sr )
1,E+07
1,E+05
1,E+04
1,E+03
1990
1995
Année
Year
2000
2005
-8
-6
-4
-2
0
2
4
6
the solar
Année duYear
cycleofsolaire
(mincycle
solaire =0)
 Being given the quality and the quantity of the data , only the first five energy channels will be
used in the MEO model: 0.28 MeV, 0.40 MeV, 0.56 MeV, 0.80 MeV and 1.12 MeV.
Construction of the model : Method used
MEO model
• Limitation: - only one solar cycle, not full
- small statistic
 Development of a mean model over a solar cycle and not dependant of the
year of the solar cycle.
• Definition of an error bar
Max flux ( * error bar)
Mean flux
Min flux ( / error bar)
E > 400 keV
1,00E+07
Flux (cm-2.s-1.sr-1)
(representing the uncertainties of the
measurements and the fluctuations of flux
levels from one solar cycle to another) :
0.018 *E(keV) + 1.76
1,00E+06
1,00E+05
-8
-6
-4
-2
0
2
year of solar cycle
4
6
Construction of the model : Comparison with POLE model
• Comparison between MEO model at 5.5 < L < 6.5 and POLE model at
geostationary orbit (yearly averaged electrons fluxes in function of the year of the solar cycle)
> 1.12 MeV
> 0.28 MeV
1,00E+05
Flux (cm-2.sr-1.s-1)
Flux (cm-2.sr-1.s-1)
1,00E+06
1,00E+05
MEO L~6
POLE
GPS
L=6
POLE
-6
-4
1,00E+03
MEO L~6
POLE
GPSPOLE
L=6
1,00E+02
1,00E+04
-8
1,00E+04
-2
0
2
Year of solar cycle
4
6
-8
-6
-4
-2
0
2
Year of solar cycle
 There is a good agreement between electron flux levels deduced from MEO
model near geostationary orbit (5.5 < L< 6.5) and the one deduced from POLE
model.
4
6
Construction of the model : Comparison NASA AE8 model
• Comparison between MEO model and NASA AE8 model along GNSS orbit
sur un
cycle
solaire
(11(11
ans)
Flux
d'électrons
Electrons
flux over
one
solar
cycle
years)
1,0E+07
Flux (cm-2.s-1.sr-1)
1,0E+06
1,0E+05
1,0E+04
MEO cas
: mean
case
MEO:
moyen
MEO cas
: best
case
MEO:
favorable
1,0E+03
1,0E+02
X
1,0E+01
1,0E+00
0,1
MEO cas
: worst
case
MEO:
pire
AE8(7
(7ans
years
MAX,
4 years
MIN)
AE8
MAX,
4 ans
MIN)
1
10
Energie(MeV)
(MeV)
Energy
 Mean electrons flux over a solar cycle deduced from MEO
model is similar to electrons flux deduced from NASA AE8
model.
Conclusions
 MEO model (GNSS like orbit) :
- from 0.28 MeV to 1.12 MeV
- based on 14 years of GPS Navstar data (NS-18, NS-24, NS-28 and NS-33) and on
GLONASS-94 data
- electron fluxes deduced from the model are not dependent of the year of the solar
cycle (mean model over 11 years).
 Comparison between MEO model and NASA AE8 model:
- Mean electrons flux deduced from MEO model is equivalent to the one deduced
from AE8 model.
Perspectives
 Improvement of MEO model in order to evaluate electrons fluxes in
function of the year of solar cycle (better statistics is essential: more
data is needed)
Data Analysis : Background
Definition of the background
Background of
the instrument
Rapport
Ratio
Rapport (avec
background/sans
fluxFlux
avecwith
background
/ fluxwithout
sans background
bg
/ Flux
bgbackground)
Importance of the background
22
1,8
1.8
1.6
1,6
1990
1,4
1.4
1991
1992
1,2
1.2
11
0.8
0,8
00
0,5
0.5
11
1,5
1.5
22
2.5
2,5
33
3,5
3.5
Energie
(MeV)
Energy
(MeV)
Energie (MeV)
Background
has been
removed
In order to analyze the importance of the background
in yearly averaged electron fluxes (used to construct the
model), two averages have been calculated: one by
taking into account the background and one without
background.
Ratio is less than a factor 2  Background plays a
minor role in yearly averaged fluxes.
In the model we use yearly averaged flux with background: a
small overestimation of electrons fluxes in the model is
more secure than a underestimation